Method and apparatus for preventing plasma formation

ABSTRACT

A plasma etching device is described in which gas is introduced into a reaction chamber through holes in a gas distribution plate. An electrode ignites the source gas into a plasma by capacitive coupling, and sustains the plasma by inductive coupling. A localized shield structure is provided which suppresses the electric field in locations in or near the holes of the gas distribution plate. Thus, plasma ignition in or near these holes is prevented, and hole lightup effects are avoided. By virtue of eliminating hole lightup, improved flexibility in gas distribution plate design and alignment is provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.08/935,441, filed Sep. 23, 1997, which issued as U.S. Pat. No.6,123,802.

TECHNICAL FIELD

This invention relates generally to plasma etching during integratedcircuit fabrication, and more particularly to methods and apparatus forpreventing undesirable plasma formation during such fabrication.

BACKGROUND OF THE INVENTION

Integrated circuits are commonly fabricated on and within a surfaceregion of a semiconductor substrate, such as a wafer of silicon. Duringsuch fabrication, various layers are produced within the substrate ordeposited thereon. Some of these layers are then sized and dimensionedto form desired geometric patterns by means of various etchingtechniques. Such etching techniques include “wet” etching techniques,which typically use one or more chemical reagents brought into directcontact with the substrate, or “dry” etching techniques, such as plasmaetching.

Numerous plasma-based etching techniques are known in the art, includingwhat is commonly called the plasma etching mode, as well as reactive ionetching and reactive ion beam etching. In any of the wide variety ofplasma etching techniques, a plasma is created by introducing a gas intoa chamber in which one or more electrodes (commonly driven by an RFgenerator) generate the plasma by disassociation of the gas moleculesinto various ions, free radicals and electrons. The plasma then reactswith the material being etched from the semiconductor substrate.

FIG. 1 depicts a prior art plasma etching device 10, such as the Lam9100, manufactured by Lain Research, Inc. The plasma etching device 10includes an electrode such as a planar coil electrode 12, which ispositioned proximate to a plate or window 14 formed from a suitabledielectric material. The window 14 is spaced apart from a dielectric gasdistribution plate 16, with the space sealed by an O-ring 18. Sourcegases from which the plasma is to be generated are inserted into the gapformed between the window 14 and gas distribution plate 16. The sourcegases then diffuse through a plurality of openings or holes 20 includedin the gas distribution plate 16 into a reaction chamber 22—the wall ofwhich is typically grounded.

A high-voltage RF signal is applied to the planar coil electrode 12 andignites a plasma within the reaction chamber 22. Ignition of the plasmaoccurs primarily by capacitive coupling of the electrode 12 with thesource gas, due to the large magnitude voltages applied to theelectrode. Once ignited, the plasma is sustained by electromagneticinduction effects associated with a time-varying magnetic field causedby the RF signal applied to the electrode 12.

A semiconductor wafer 24 is positioned within the reaction chamber 22and is supported by a wafer platform or chuck 26. The chuck 26 istypically electrically biased to provide ion energies impacting thewafer 24 which are approximately independent of the RF voltage appliedto the electrode 12. Volatile reaction products, as well as plasmaspecies which did not interact with the wafer 24, are then pumped out ofthe reaction chamber 22, usually by means of a vacuum pump.

One disadvantage of devices such as the plasma etching device 10 of FIG.1 is the existence of “hole lightup” effects. The capacitive coupling ofthe electrode 12 with the gases and/or plasma in the reaction chamber 22can create electric fields of sufficient strength to ignite plasmas inor near the holes 20 of the gas distribution plate 16. This causes anumber of problems. For example, when etching dielectric layers on thesemiconductor wafer 24, source gases such as fluorocarbons are used, andthe hole lightup effects cause polymer deposition in or near the holes20 and on the window 14. In the case of particle deposition in or nearthe holes 20, the distribution of source gases into the reaction chamber22 can be changed, resulting in (among other things) a potential lack ofuniformity in the etching process occurring within the chamber. Thosepolymers or other materials deposited on the window 14 may ultimatelyflake off, resulting in particle contamination within the reactionchamber 22. Additionally, energy that was intended to ignite plasmawithin the reaction chamber 22 is instead wasted in the plasma ignitionassociated with hole lightup.

To avoid hole lightup effects, the current approach includes carefulpositioning, configuring, and sizing of the holes 20 included in the gasdistribution plate 16. The holes 20 not positioned directly belowportions of the planar coil electrode 12 suffer from lesser hole lightupeffects than those holes positioned approximately below the electrode.As such, careful alignment and positioning of the holes 20 relative tothe electrode 12 is required. Even so, some hole lightup effects stilloccur, resulting in deposition of particles and wear on portions of theholes 20. The gas distribution plate is not, however, readily moved orrotated to distribute these effects, because such movement is difficultto implement within the alignment constraints. Therefore, hole lightupeffects and the constraints caused by minimizing such effects result inlower useful lifetimes for plasma etching device components such as thegas distribution plate 16. Furthermore, the location and configurationof the holes 20 cannot be designed for optimal process performance, dueto the design constraints imposed by hole lightup effects.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the present invention a plasmaetching device for etching selected materials during integrated circuitfabrication is provided. The plasma etching device includes a reactionchamber adapted to receive the selected materials. The plasma etchingdevice also includes gas flow structure adjoining the reaction chamberand including an opening through which gas can flow into the reactionchamber. An electrode is operable to produce an electromagnetic fieldfor application to the gas within the reaction chamber to ignite aplasma therewithin. A shield structure is provided which is operable andpositioned to suppress the electromagnetic field in a location proximateto and within the opening to prevent plasma formation therewithin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a plasma etching device inaccordance with the prior art.

FIG. 2 is a partial cross-sectional view depicting a plasma etchingdevice in accordance with an embodiment of the present invention.

FIG. 3 is a partial cross-sectional view depicting a portion of a firstembodiment of a shield structure included in the plasma etching deviceof FIG. 2.

FIG. 4 is a partial cross-sectional view depicting a portion of a secondembodiment of the shield structure included in the plasma etching deviceof FIG. 2.

FIG. 5 is a top, plan view depicting a third embodiment of the shieldstructure included in the plasma etching device of FIG. 2.

FIG. 6 is a block diagram depicting an etching system which includes theplasma etching device of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various embodiments of thepresent invention. However, one skilled in the art will understand thatthe present invention may be practiced without these details. In otherinstances, well-known structures associated with plasma etching deviceshave not been shown in detail in order to avoid unnecessarily obscuringthe description of the embodiments of the invention.

FIG. 2 depicts a plasma etching device 30 in accordance with anembodiment of the present invention. The plasma etching device 30largely includes components also included in the plasma etching device10 described above in connection with the prior art. However, incontrast with the prior art approach, the plasma etching device 30includes a shield structure 32 having a plurality of local shields 34positioned in locations corresponding to the holes 20 of the gasdistribution plate 16. The shield structure 32 is electrically connectedto a source of controlled electric potential, such as a fixed potentiallike ground potential 36 or a variable potential like an RF potential,as desired. The local shields 34 provide a localized blocking of thecapacitive coupling with the electrode 12, to a level sufficient tosuppress electromagnetic field strengths that cause hole lightupeffects.

The shield structure 32 does not, however, globally block the capacitivecoupling of the electrode 12 with the gases contained in the reactionchamber 22. Such global capacitive coupling is desirable because ithelps control the effects of ion bombardment on dielectric surfaces(such as the gas distribution plate 16). Further, electrostatic couplingof the electrode 12 with the gases contained in the reaction chamber 22is, in fact, the mechanism by which ignition of the plasma occurs.Although inductive ignition of plasmas is possible, readily availableequipment for plasma etching generates magnetic fields of strengthssufficient only to sustain ignited plasmas, and relies instead oncapacitive coupling for actual ignition of those plasmas. Thus, a shieldstructure which does not deleteriously affect plasma ignition within thereaction chamber 22, while suppressing hole lightup plasma effects,provides a number of advantages over the prior art.

FIG. 3 is a diagram which depicts a detail of one embodiment of theshield structure 32. In this embodiment, each of the local shields 34 ispositioned between the electrode 12 and the window 14 at locationsapproximately above a corresponding one of the holes 20 in the gasdistribution plate 16. A suitable electrical insulation structure orlayer 38 separates the electrode 12 from direct physical contact withthe shield structure 32. FIG. 4 shows a second embodiment, in which thelocal shields 34 are positioned on the opposite surface of the window 14at locations below the electrode 12 and approximately above thecorresponding hole 20. As shown in FIG. 4, certain of the holes 20 maynot be positioned beneath a section of the electrode 12, in which case alocal shield 34 need not be provided. However, providing and positioninglocal shields 34 at locations corresponding to each of the holes 20 canbe readily accomplished and will provide increased protection againsthole lightup effects, even in those holes in which such effects areexpected to be minimal in the absence of shielding.

FIG. 5 is a top view showing a third embodiment of the shield structure32. In this case, each of the local shields 34 is annular in shape,which allows location of the shield structure immediately adjacent tothe gas distribution plate 16. The annular openings provided in each ofthe local shields 34 allow source gases to flow into the openings 20 andinto the reaction chamber 22 (see FIG. 2). As long as the annularopening in the local shield 34 is of a size that is small relative tothe plasma sheath width, the requisite electrostatic shield effects willbe provided. Again, as discussed above in connection with FIG. 4 (and asequally applicable to the embodiment depicted in FIG. 3), a local shield34 need not be provided for each of the holes 20, but only for thoseholes positioned proximate to sections of the electrode 12. As depictedin FIG. 5, each of the local shields 34 is electrically connected to theothers and to ground potential 36.

In plasma etching devices such as the Lam 9100, the holes 20 included inthe gas distribution plate 16 are approximately 0.020 inches indiameter. Given the thicknesses of the dielectric window 14, the gasdistribution plate 16, and the width of the gap therebetween, localshields 34 of approximately less than ½ inch in diameter should besufficient to provide the desired shielding characteristics. However,those skilled in the art will appreciate a number of alternativegeometrical configurations and sizes of local shield structures (inaddition to those described above in connection with FIGS. 3-5) that canbe employed with plasma etching devices like the Lam 9100 or adapted foruse with other plasma etching devices.

FIG. 6 is a block diagram which depicts the major components of anetching system 40 in accordance with an embodiment of the presentinvention. The etching system 40 includes the plasma etching device 30having the electrode 12. A plasma is generated from source gases, whichare provided by a gas supply 42. The gas supply 42 is coupled to theplasma etching device 30 by a gas control panel 44, which selects andcontrols the flow of source gases into the plasma etching device. Thehigh voltage signal applied to the electrode 12 is provided by a powergenerator, such as an RF generator 46, which is coupled with theelectrode by an impedance matching network 47, as is well known in theart. Volatile reaction products, unreacted plasma species, and othergases are removed from the plasma etching device 30 by a gas removalmechanism, such as a vacuum pump 48 and throttle valve 50.

A number of advantages are provided in accordance with the variousembodiments of the invention described above. The shield structure 32suppresses local electric fields which cause the undesired hole lightupeffects, but does not significantly block the capacitive couplingnecessary to ignite the desired plasmas within the reaction chamber 22.By avoiding hole lightup, the disadvantages of changed gas distributionand etching process contamination are avoided. Furthermore, thealignment and dimension constraints of the current state of the art maybe considerably relaxed. Thus, for example, the gas distribution plate16 can be regularly rotated or otherwise moved to distribute wear. Theuseful life of the gas distribution plate is then significantly extendedin comparison to prior art plasma etching devices. As a further example,the gas distribution holes 20 could be increased in size relative toprior art designs, which may provide improved process results, includingmore uniform etching of the semiconductor wafer 24 positioned within thereaction chamber 22. Those skilled in the art will also appreciate thatthe principle of local shielding in accordance with the presentinvention can be applied in other locations within plasma etchingdevices, such as at the edges of coil electrodes where undesiredcoupling to other parts of the reaction chamber might occur.

It will be appreciated that, although embodiments of the invention havebeen described above for purposes of illustration, various modificationsmay be made without deviating from the spirit and scope of theinvention. For example, the particular configuration and position of thelocal shields 34 described above should not be construed to unduly limitthe configuration and location of other similarly adapted shieldstructures which accomplish the purpose of local suppression of electricfields and their untoward effects. Those skilled in the art will alsoappreciate that the local shield structure and method taught inaccordance with the present invention can be applied to devices andmethods other than those associated with plasma etching of semiconductormaterial during integrated circuit fabrication. Also, those skilled inthe art will appreciate that other localized shield structures andmethods may be suitably adapted to function substantially as theparticular electrostatic shield structures and methods described above.Indeed, numerous variations are well within the scope of the invention.Accordingly, the scope of the invention is not limited by the disclosureof particular embodiments, and terms used in the following claims shouldnot be construed to limit the invention to these embodiments. Instead,the scope of the invention is determined entirely by the followingclaims.

What is claimed is:
 1. A plasma etching device for etching selectedmaterials during integrated circuit fabrication, comprising: a reactionchamber adapted to receive the selected materials; an electrode operableto produce an electromagnetic field for application to the gas withinthe reaction chamber to ignite a plasma therewithin; a gas flowstructure adjoining the reaction chamber and positioned between theelectrode and the reaction chamber including an opening through whichgas flows into the reaction chamber; and a shield structure interposedbetween the electrode and the opening operable and positioned tosuppress the electromagnetic field in a location adjacent to and withinthe opening to prevent plasma formation therewithin.
 2. The plasmaetching device of claim 1 wherein the gas flow structure includes firstand second dielectric slabs with a gap therebetween, the firstdielectric slab positioned adjacent to the electrode, and the seconddielectric slab having the opening and positioned adjacent to thereaction chamber, the gas flowing through the gap into the opening andinto the reaction chamber, and wherein the shield structure isinterposed within the gap adjacent to the first dielectric slab andproximate to the opening in the second dielectric slab.
 3. The plasmaetching device of claim 1 wherein the gas flow structure includes firstand second dielectric slabs with a gap therebetween, the firstdielectric slab positioned adjacent to the electrode, and the seconddielectric slab having the opening and positioned adjacent to thereaction chamber, the gas flowing through the gap into the opening andinto the reaction chamber, and wherein the shield structure ispositioned within the gap adjacent to the opening in the seconddielectric slab.
 4. The plasma etching device of claim 1 wherein theelectrode is a coil electrode.
 5. The plasma etching device of claim 1wherein the electrode is a planar coil electrode.
 6. The plasma etchingdevice of claim 1 wherein the electrode is operable to produce anelectric field to ignite the plasma.
 7. The plasma etching device ofclaim 1 wherein the electrode is operable to produce an electric fieldto ignite the plasma, and wherein the shield structure includes anelectrostatic shield to suppress the electric field in the locationadjacent to and within the opening to prevent plasma formationtherewithin.
 8. The plasma etching device of claim 1 wherein the gasflow structure includes a plurality of openings, and wherein the shieldstructure includes a plurality of local shields, each of the openingshaving a corresponding one of the local shields positioned adjacentthereto.
 9. The plasma etching device of claim 1 wherein the gas flowstructure includes a plurality of openings, and wherein the shieldstructure includes a plurality of local shields, selected ones of theopenings having a corresponding one of the local shields positionedadjacent thereto.
 10. A plasma etching device for etching selectedmaterials during integrated circuit fabrication, comprising: a chamberadapted to receive gas therewithin; an electromagnetic field sourcecoupled with the chamber and operable to apply an electromagnetic fieldto the gas to ignite and sustain a plasma within the chamber; a gasdistribution plate including a plurality of openings operable to passthe gas into the chamber positioned adjacent to the chamber and betweenthe chamber and the electromagnetic field source, and; a shieldstructure including a plurality of local shields, and each adapted to becoupled to a corresponding source of controlled electric potential,wherein each of the local shields is positioned in a location adjacentto a corresponding one of the openings, the local shields substantiallysuppressing the electromagnetic field in locations adjacent to the localshields.
 11. The plasma etching device of claim 10 wherein each of thelocal shields is of a substantially circular disk shape.
 12. The plasmaetching device of claim 11 wherein the electromagnetic field sourceincludes an electrode positioned adjacent to the chamber, and whereineach of the local shields is positioned in a location adjacent to theelectrode and adjacent to a corresponding one of the openings.
 13. Theplasma etching device of claim 12 wherein each of the local shields isof a substantially circular disk shape.
 14. The plasma etching device ofclaim 10 wherein the electromagnetic field source includes an electrodepositioned adjacent to the chamber, and wherein each of the localshields is positioned adjacent to a corresponding one of the openings.15. The plasma etching device of claim 14 wherein each of the localshields is of substantially annular shape.
 16. The plasma etching deviceof claim 10 wherein the plurality of local shields are electricallycoupled to one another, and wherein the corresponding source ofcontrolled electric potential is a source of approximately constantelectric potential.
 17. The plasma etching device of claim 10 whereinthe plurality of local shields are electrically coupled to one anotherand to ground potential.
 18. The plasma etching device of claimed 10wherein the electromagnetic field source includes an electrodepositioned adjacent to the chamber.
 19. The plasma etching device ofclaim 10 wherein the electromagnetic field source includes a coilelectrode positioned adjacent to the chamber.
 20. The plasma etchingdevice of claim 10 wherein the electromagnetic field source includes aplanar coil electrode positioned adjacent to the chamber.
 21. The plasmaetching device of claim 10 wherein the chamber includes a single cavityin which the plasma is ignited and which is adapted to receive theselected materials for etching.
 22. A method of forming a plasma from agas contained within a chamber, comprising the steps of: introducing asource gas into the chamber through a gas flow opening; applying anelectromagnetic field to the chamber of sufficient magnitude to ignite aplasma therewithin; and suppressing the magnitude of the appliedelectromagnetic field at a selected location adjacent to and within thegas flow opening to prevent ignition of a plasma at the selectedlocation.
 23. The method of claim 22 wherein the step of suppressing themagnitude of the electromagnetic field at a selected location adjacentto and within the gas flow opening includes the step of shielding theselected location.
 24. The method of claim 22 wherein the step ofapplying an electromagnetic field to the chamber of sufficient magnitudeto ignite a plasma therewithin includes the step of applying an electricfield to ignite the plasma.
 25. The method of claim 22 wherein the stepof applying an electromagnetic field to the chamber of sufficientmagnitude to ignite a plasma therewithin includes the step of applyingan electric field to ignite the plasma, and wherein the step ofsuppressing the magnitude of the electromagnetic field at a selectedlocation adjacent to and within the gas flow opening includes the stepof electrostatically shielding the selected location.
 26. The method ofclaim 22 wherein the step of applying an electromagnetic field to thechamber of sufficient magnitude to ignite a plasma therewithin includesthe step of applying a time-varying electric field to ignite the plasma.27. The method of claim 22 wherein the step of applying anelectromagnetic field to the chamber of sufficient magnitude to ignite aplasma therewithin includes the step applying a time-varying magneticfield to the chamber to sustain the ignited plasma.
 28. In a plasmaetching device including a gas distribution device having an openingthrough which gas flows into a reaction chamber, the reaction chamberadapted to receive material to be etched by a plasma formed byapplication of an electromagnetic field to the gas, a method ofpreventing plasma formation at a region surrounding the opening andwithin the opening, comprising the step of suppressing theelectromagnetic field in a location adjacent to the opening.
 29. Themethod of claim 28 wherein the step of suppressing the electromagneticfield in a location includes the step of shielding the location.
 30. Themethod of claim 28 wherein the step of suppressing the electromagneticfield in a location includes the step of electrostatically shielding thelocation.
 31. In a plasma etching device including a gas distributionplate having a plurality of openings through which gas flows into areaction chamber, the reaction chamber adapted to receive material to beetched by a plasma formed by application of an electric field to thegas, a method of preventing plasma formation at regions surrounding theopenings and within the openings, comprising the step of suppressing theelectric field in at least one location adjacent to a corresponding oneof the openings.
 32. The method of claim 31 wherein the step ofsuppressing the electric field in at least one location includes thestep of shielding the location.
 33. The method of claim 31 wherein thestep of suppressing the electric field in at least one location includesthe step of electrostatically shielding the location.
 34. An etchingsystem for etching selected materials, comprising: a gas supply operableto provide source gas; a power generator operable to provide a powersufficient to produce a plasma from the source gas; and a plasma etchingdevice coupled with the gas supply and with the power generator, andincluding: a reaction chamber adapted to receive the selected materials;a gas flow structure adjoining the reaction chamber and operable toreceive the source gas provided by the gas supply, the gas flowstructure including an opening through which the source gas flows intothe reaction chamber; an electrode operable to receive the powerproduced by the power generator and correspondingly producing anelectromagnetic field for application to the source gas within thereaction chamber to ignite a plasma; and a shield structure operable andpositioned to suppress the electromagnetic field in locations adjacentto and within the opening to prevent plasma formation in theselocations.
 35. The etching system of claim 34 further comprising a gasremoval mechanism coupled with the plasma etching device and operable toremove gas therefrom.
 36. The etching system of claim 35 wherein the gasremoval mechanism includes a vacuum pump.
 37. The etching system ofclaim 34 further comprising a gas control panel coupling the gas supplywith the plasma etching device and operable to control the flow ofsource gas into the plasma etching device.
 38. The etching system ofclaim 36 wherein the power generator is an RF generator.